Metering devices for metering hypochlorite compounds, in particular in the form of calcium hypochlorite, are used for a multiplicity of disinfecting tasks in aqueous systems, for example in drinking water treatment, the treatment of swimming and bathing pool water, the disinfection of process and service water in industry and CIP applications (cleaning-in-place applications), such as, for example, the cleaning of plants in the food and drinks industry or of ultrafiltration systems (UF systems).
Since calcium hypochlorite is a solid which is generally present as dry granules, it is generally known to dissolve the calcium hypochlorite before use in a dissolution container (dissolution container method). In this case the dissolution container is manually charged with calcium hypochlorite granules and exposed to a dissolving water stream. The calcium hypochlorite from the calcium hypochlorite charge passes in part into solution in such a manner that the dissolution container is filled to a defined liquid level with calcium hypochlorite solution. Via an inoculation apparatus, the calcium hypochlorite solution is then withdrawn from the dissolution container and introduced into the water stream that is to be disinfected.
A disadvantage with this solution is that when the dissolution container is manually charged with calcium hypochlorite, a calcium hypochlorite dust emission which is hazardous to health can occur. It must therefore be charged using suitable workers' protective equipment (breathing protection etc). In addition, when the dissolution container is being charged with water or is being refilled with calcium hypochlorite granules, sediment from the bottom of the dissolution container can be swirled up, and this can impair the functioning of fittings downstream of the inoculation water apparatus. Metering pumps, injectors and inoculation water fittings must therefore be cleaned regularly manually. In addition, it is disadvantageous that the resultant dissolution residues at the bottom of the dissolution container form a calcium hypochlorite bed mixed with dissolution residues, which bed remains in the dissolution container. The mixed bed prevents determination of the filling level of the calcium hypochlorite stock present and must be washed away, usually into the sewer system, at regular intervals. Since the contents of the dissolution container, consisting of still undissolved calcium hypochlorite and the prepared solution, are disposed of completely in this case, relatively large amounts of chlorine can pass into the sewer system.
For automating charging with calcium hypochlorite, DE 195 07 329 A1 discloses a device for metering calcium hypochlorite, in which the calcium hypochlorite granules are transported from a storage appliance into the dissolution container by means of a pneumatic conveyor. Particulate residues are dissolved in this solution by adding hydrochloric acid (mixing method). This prevents the functioning of the metering appliances arranged downstream of the calcium hypochlorite dissolution container from being adversely affected by particulate residues, but by adding hydrochloric acid, the chloride loading in the water stream that is to be disinfected is increased extremely. The addition of acid to the calcium hypochlorite solution can therefore lead to release of chlorine gas from the dissolution appliance. In addition, in the case of such pneumatic conveyors, in particular in the event of damage to the filters, calcium hypochlorite dust which is a health hazard can likewise escape. Such semiautomatic charging systems having dry conveyors are, in addition, complex in terms of fabrication and are susceptible to faults owing to the risk of blockage of the conveyor.
In addition, U.S. Pat. No. 4,842,729 discloses a water treatment system in which a receiver is provided for a basket having water treatment tablets branching off in the manner of a T piece from the side of the water line conducting the water that is to be treated. By means of a lid which can be screwed onto the basket receiver, the basket can be lowered into the water line pretensioned against a spring, or exchanged after opening the lid. On exchange of the basket, however, the operator is again exposed to the water treatment tablet components that are hazardous to health.
U.S. Pat. No. 5,447,641 discloses a chlorine addition unit for treating poultry drinking water. The unit possesses a housing in which calcium hypochlorite is arranged in solid form and is dissolved in water. The housing is closed on its open side with a removable lid. In order to recharge the housing with calcium hypochlorite tablets, the lid is opened and the tablets are charged by the operator, in which case the operator comes into contact with the calcium hypochlorite.
U.S. Pat. No. 6,298,871 B1 discloses a feeder unit for, in particular, calcium hypochlorite, which feeder unit comprises a canister for receiving calcium hypochlorite tablets. The canister is introduced into a container and this container is closed by means of a screw closure. In order to refill the container with calcium hypochlorite tablets, the screw closure is opened and the tablets are charged by the operator, in which case the operator comes into contact with the calcium hypochlorite.